Nanoindentation inputfile

Hello Everyone,

I’m working on Nanoindentation of CNT-Epoxy Polymer.
Made Input file for Indentation process as shown below.

Hello Everyone,

I'm working on Nanoindentation of CNT-Epoxy Polymer.
Made Input file for Indentation process as shown below.
----------------------------------------------------------------------------------------------------------
INPUT FILE:
#Region for Indentation
region 2 block INF INF INF -30 INF INF
group frozen region 2
group mobile subtract all frozen

fix 50 frozen setforce 0.0 0.0 0.0

compute 30 all ke/atom
compute 40 all pe/atom pair

#Indentation Process:
timestep 0.0002
variable y equal 156-0.5*dt*step
fix 3 all indent 10 sphere 0 v_y 0 80 units box
fix_modify 3 energy yes

compute stress mobile stress/atom NULL ke pair

fix dump mobile ave/spatial 5000 1 5000 y lower 70 c_stress[1]
c_stress[2] c_stress[3] c_stress[4] c_stress[5] c_stress[6] file stress.dat
units lattice

run 50000

----------------------------------------------------------------------------------------------------------------
But the output file stress.dat, generating same stress values for each time
step

for example:
sigmaxx =0.001, sigmayy=0.004 and so at step 1000
sigmaxx =0.001, sigmayy=0.004 and so at step 5000

Can any explain me, if there is any error in my input file?

better you figure it out yourself. please have a close look at the log
file that is generated and pay attention to the warnings given in
there.

axel.

Dr. Axel,

Thank you for your quick reply!

I have checked the log file, I didn’t get any warnings, everything is good.

Thank you again!

Ashok Kumar Bevara

Dr. Axel,

Thank you for your quick reply!

I have checked the log file, I didn’t get any warnings, everything is good.

Look again. There has to be one.
Your quoted input has no time integration and your report of unchanged stress is consistent with that.

Otherwise, you would have to have omitting important parts of your input and nobody can help you with what you don’t show.

Dr.Axel,

Greetings!

Thank you respons.

Its really helped me.

I’ve used time integration as you suggested (fix NVT)
also I read in mailing-list that lattice should be mandatory for Nanoindentation process.
So I’ve used “lattice 3.52”(3.52 random value), then my simulation running and giving stress values
But, I didn’t get exactly why do we need lattice and how to find values for lattice

after this, May I know how to find the forces acting by indenter on each atom at each step (atoms means, which are affecting by indenter during particular time step)

Thanks in advance!

Bevara

Dr.Axel,

Greetings!

Thank you respons.

Its really helped me.

I've used time integration as you suggested (fix NVT)
also I read in mailing-list that lattice should be mandatory for
Nanoindentation process.

no, it isn't.

So I've used "lattice 3.52"(3.52 random value), then my simulation running
and giving stress values

that doesn't make sense.

But, I didn't get exactly why do we need lattice and how to find values for
lattice

unless you are using a very outdated version of LAMMPS, there is a
default initialization for the lattice command in such a way that
lattice and box units are the same. for old versions, some commands
defaulted to lattice units and thus created an error message, if no
lattice was assigned, or sometimes unexpected behavior, if a lattice
was assigned and coordinates/parameters were input in box units, but
the command was given without a flag indicating this, and thus using
lattice units instead.

after this, May I know how to find the forces acting by indenter on each
atom at each step (atoms means, which are affecting by indenter during
particular time step)

you cannot. you can only access the total force vector and the energy.
see the fix indent documentation.

Dr. Axel,

Thank you for reply.

I’m using 9Dec14 version. So, don’t I need to use lattice command?

And may I know how to compute this total force vector by indent

Thanks in advance!

Bevara

Dr. Axel,

Thank you for reply.

I'm using 9Dec14 version. So, don't I need to use lattice command?

RTFM!

And may I know how to compute this total force vector by indent

RTFM!!

Fix indent produces force on the indenter as an output,

see it’s doc page.

Steve

Dr. Steve,

Thanks for reply.

I have gone through manual.

Sorry to ask this question

I’ve used dump command as shown below to dump forces produced by indenter

like “dump 7 mobile dum_forces*.txt mass type fx fy fz”

But I think group ID is not correct.

Can you please help me to what to use for group ID?

INPUT FILE:
#Region for Indentation
region 2 block INF INF INF -30 INF INF
group frozen region 2
group mobile subtract all frozen

fix 50 frozen setforce 0.0 0.0 0.0

compute 30 all ke/atom
compute 40 all pe/atom pair

reset_timestep 0
timestep 0.0002
fix 5 all nvt temp 300.0 300.0 75 drag 1.5
variable y equal 156-0.5dtstep
fix 3 all indent 10 sphere 0 v_y 75 80 units box
fix_modify 3 energy yes

dump 7 mobile dum_forces*.txt mass type fx fy fz

fix dump mobile ave/spatial 5000 1 5000 y lower 70 c_stress[1] c_stress[2] c_stress[3] c_stress[4] c_stress[5] c_stress[6] file stress.dat units lattice

run 50000

Thank you in advance,

Bevara

Please keep in mind that we normally don’t debug input files.

What Steve is trying to tell you is that fix indent outputs force on the indenter so you don’t need to use dump that you did. Please see fix indent doc page for details.

Ray